Storage architecture for virtual machines

ABSTRACT

Some embodiments of the present invention include a method comprising: accessing units of network storage that encode state data of respective virtual machines, wherein the state data for respective ones of the virtual machines are stored in distinct ones of the network storage units such that the state data for more than one virtual machine are not commingled in any one of the network storage units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.15/701,390, filed Sep. 11, 2017, which is a continuation of prior U.S.application Ser. No. 14/937,453, filed Nov. 10, 2015, which is acontinuation of prior U.S. application Ser. No. 11/960,460, filed Dec.19, 2007, which claims the benefit of U.S. Provisional Application No.60/871,234, filed Dec. 21, 2006, U.S. Provisional Application No.60/884,568, filed Jan. 11, 2007, and U.S. Provisional Application No.60/886,072, filed Jan. 22, 2007.

This application is related to U.S. patent application Ser. No.11/960,491, filed Dec. 19, 2007 and issued as U.S. Pat. No. 9,098,347,and to U.S. patent application Ser. No. 11/960,524, filed Dec. 19, 2007and issued as U.S. Pat. No. 9,354,927 and entitled “SECURING VIRTUALMACHINE DATA”.

The content of each of the above applications is hereby incorporated byreference in its entirety.

BACKGROUND Field of the Invention

One or more embodiments of the present invention relate to virtualmachines and, more specifically, to methods for supporting virtualmachines with respective units of storage.

Description of the Related Art

In general, state data for a virtual machine may be encoded in some formof computer readable media. In some cases, storage local to anunderlying hardware platform can be used. In some cases, storage arraytechnology may be used to share pools of underlying storage amongstmultiple computational systems. Regardless of the storage technologiesused, file system constructs are typically employed to mediate access tostored information. Methods are desired whereby at least certain aspectsof the virtual machine state may be encoded and accessed without much ofthe complexity and overhead usually associated with an intermediary filesystem.

SUMMARY

Some embodiments of the present invention address one or more of theabove-identified needs. In particular, one embodiment of the presentinvention includes a method comprising: accessing units of networkstorage that encode state data of respective virtual machines, whereinthe state data for respective ones of the virtual machines are stored indistinct ones of the network storage units such that the state data formore than one virtual machine are not commingled in any one of thenetwork storage units.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an example of a system that incorporates network storagesystem capabilities into virtual machine provisioning.

FIG. 1B depicts preparation of allocated network storage units in thesystem of FIG. 1A.

FIG. 2 depicts a flowchart of an embodiment for partial integration ofvirtual machine provisioning and storage provisioning.

FIG. 3 depicts a flowchart of an embodiment for allocation of multiplestorage units for a virtual machine.

FIG. 4 depicts an organization of a network storage unit that encodesstate data for a single virtual machine.

FIG. 5 depicts an organization of a network storage unit that encodesvirtual machine data with the exception of a virtual primary disk.

FIG. 6 depicts an organization of a network storage unit that encodesvirtual machine data including virtual primary disk data.

FIG. 7 depicts an organization of a network storage unit that encodesvirtual machine data including multiple virtual disks.

FIG. 8A depicts a virtualization system securing non-disk data. FIG. 8Bdepicts an organization of an encoding of a storage unit to securenon-disk data.

FIG. 9 depicts an embodiment of a virtualization system configurationreferred to as an “OS hosted” virtual machine configuration.

FIG. 10 depicts an embodiment of a virtualization system configurationreferred to as a “non-OS hosted” virtual machine configuration.

FIG. 11 depicts an embodiment of a virtualization layer interceptingdisk access requests from a guest of a virtual machine.

FIG. 12 depicts an embodiment of snapshot operations for a virtualmachine.

FIG. 13 depicts a flowchart of an embodiment of a method for activatinga snapshot.

FIG. 14 depicts a flowchart of an embodiment of a method for automaticdiscovery of virtual machines.

FIG. 15 depicts a flowchart of an embodiment of a method for performinga move of a virtual machine.

FIG. 16 depicts an embodiment of a local move command operation for avirtual machine.

FIG. 17 depicts an embodiment of a remote move command operation for avirtual machine.

FIG. 18 depicts an embodiment of a clone command operation for a virtualmachine.

FIG. 19 depicts a flowchart of an embodiment of a method for migratingvirtual machine data.

FIG. 20 depicts a collection or cluster of computational systems inwhich an embodiment of the present invention may be used.

The use of the same reference symbols in different figures indicatessimilar or identical items.

DESCRIPTION OF EMBODIMENT(S)

In accordance with one or more embodiments of the present invention,methods for encoding data used by virtual machines allow for certaintypes or portions of virtual machine data to be encoded, for each suchvirtual machine, in a distinct unit (or set of units) of networkstorage. In some embodiments, these methods allow a virtualizationsystem to expose data that encodes a virtual disk, while securingnon-disk data that encodes virtual machine state, virtual hardwareconfiguration and/or snapshot or checkpoint states. Typically, anencoding of virtual machine state includes backing state datacorresponding to internal states of devices, memory and other systemcomponents virtualized by or for a given virtual machine. As such, readaccess to such state date (e.g., by a guest) may leak or compromisesensitive information, while write access may afford malicious code orusers with an attractive vector for attack.

It has been discovered that by provisioning distinct units of storagefor respective virtual machines, a virtualization system can providemanagement and operation of virtual machines without use of anintermediary file system to access virtual machine state data. Such anapproach can greatly improve performance in some embodiments, and canprovide functional benefits as well. One or more units of storage areallocated to one and only one virtual machine. Typically, an indicationof the associated virtual machine is indicated in the storage units andan indication of the allocated units is indicated to a virtualizationlayer that supports the virtual machine. By allocating distinct sharedstorage units (or sets thereof) for individual virtual machines, or forparticular aspects of individual virtual machines, some embodiments inaccordance with the present invention facilitate management andoperation of virtual machines at a granularity native to the storagearchitecture.

In some embodiments, a unit of storage can be prepared or presented in amanner that secures virtual machine state data encoded therein fromundesired exposure to a guest application or operating system executingin coordination with the virtual machine, while still facilitatingaccess (e.g., by a guest computation) to other data (e.g., virtualprimary disk data) also encoded in the unit of storage. In general,undesired exposure of virtual machine state data to a guest of a virtualmachine can risk corruption of the state data and, perhaps, othernon-disk data. Whether such corruption is accidental or intentional, thecorruption can be avoided by limiting guest access to only anappropriate subset of data encoded in the storage unit.

In some virtualization system embodiments, an appropriate subsetincludes data that is exposed to the guest computation as theinformation content of a disk virtualized by the virtual machine. Insome embodiments, mutually exclusive units of storage are employed foreach virtual machine supported in a virtualization system. Typically, insuch embodiments, the storage allocated for a particular virtual machineis partitioned in such a way that the virtualization system may exposevirtual disk data, while restricting access to non-disk data (e.g.,virtual machine state data corresponding to internal states of devices,memory and other system components virtualized). Various techniques,such as encryption and/or use of offsets, may also be implemented toprevent circumvention of the restricted access. In some embodiments,partitions are organized (and partition information is manipulated) suchthat a reduced apparent size of storage that encodes both disk andnon-disk data is presented to the guest and conceals non-disk databeyond an apparent extent of the storage.

In some embodiments, functionality of storage arrays can be leveraged inthe implementation of virtual machine operations that manipulate anencoding of virtual machine state. For example, suitable codingtechniques for virtual machine state can facilitate the use of snapshot,replicate, discovery, and other storage array functionality by avirtualization layer on a virtualization system or by a virtual machinemanager to effectuate operations on, and/or manipulations of, virtualmachine state. For example, by provisioning and managing virtual machinestorage using interfaces (e.g., the block-level I/O typical of SANtechnology) and/or granularity native to the storage environment (e.g.,storage volume, logical unit number, etc.), some embodiments inaccordance with the present invention can directly exploit storagesystem functionality in support of operations such as virtual machinemigration, movement, cloning. In some embodiments, check pointing,rollback and even failover support can be efficiently supported usingfunctionality of a storage array.

Based on the description herein, it will be apparent to persons ofordinary skill in the art that the term “non-disk data” refers to datathat encodes information other than that exposed as a disk by avirtualization system or other similar software system, rather than toany exclusion of underlying storage technology. For concreteness ofdescription, an example of “non-disk data” is backing state datacorresponding to internal states of devices, memory and other systemcomponents virtualized by or for a given virtual machine. Similarly, anexample of “disk data” is information exposed to a guest application oroperating system by a virtualization system as a virtual primary(secondary, tertiary . . . ) disk. For avoidance of doubt, underlyingencodings of both disk and non-disk data may reside in media thatinclude or constitute disks.

The following describes embodiments in which virtual machine data isencoded in units of storage allocated from pooled network storage sharedamongst virtualization systems. Although network storage units provide auseful descriptive context in which to illustrate embodiments, networkstorage is not essential. Rather, based on the description herein,persons of ordinary skill in the art will appreciate that embodiments ofthe present invention may be used in the context of other storagetechnologies and configurations to selectively expose certain portionsof virtual machine state while securing and/or isolating other portions.

As used herein, the term network storage refers generally to storagesystems and storage array technology, including storage area network(SAN) implementations, network attached storage (NAS) implementations,and other storage architectures that provide a level of virtualizationfor underlying physical units of storage. In general, such storagearchitectures provide a useful mechanism for sharing storage resourcesamongst computational systems. In some cases, computational systems thatshare storage resources may be organized as a coordinated system (e.g.,as a cluster or cooperatively managed pool of computational resources orvirtualization systems). For example, in a failover cluster it may bedesirable to share (or at least failover) virtual machine access to somestorage units. Similarly, in a managed collection of virtualizationsystems, it may be desirable to migrate or otherwise transition virtualmachine computations from one virtualization system to another. In somecases, at least some computational systems may operate independently ofeach other, e.g., employing independent and exclusive units of storageallocated from a storage pool (or pools) provided and/or managed usingshared network storage.

Generally, either or both of the underlying computer systems and storagesystems may be organizationally and/or geographically distributed. Forexample, some shared storage (particularly storage for data replication,fault tolerance, backup and disaster recovery) may reside remotely froma computational system that uses it. Of course, as will be appreciatedby persons of ordinary skill in the art, remoteness of shared storage isa matter of degree. For example, depending on the configuration, networkstorage may reside across the globe, across the building, across thedata center or across the rack or enclosure.

While embodiments of the present invention, particularlycluster-organized and/or enterprise scale systems, may build upon orexploit data distribution, replication and management features of modernnetwork storage technology, further embodiments may be used in moremodest computational systems that employ network storage technology. Forexample, even a single computer system may employ SAN-type storagefacilities in its storage architecture. Thus, while some embodimentsutilize network storage that can be shared and while at least someunderlying elements thereof may be remote, persons of ordinary skill inthe art will understand that for at least some embodiments, networkstorage need not be shared or remote.

In some embodiments of the present invention, particularly those thatuse SAN-type storage arrays, block-level I/O access to virtual machinestate data can afford performance advantages. Similarly, encapsulationand/or isolation techniques are described which may be employed in someencodings of virtual machine state data to limit access (e.g., by aguest application or operating system) to underlying data. Accordingly,certain embodiments are described in which non-commingled, encapsulatedrepresentations of virtual machine state are maintained in distinctstorage volumes (or LUNs) of a SAN. Nonetheless, other embodiments,including those that use NAS-type or filesystem-mediated accessmechanisms may still allow a virtualization system to leverage storagesystem functionality in support of operations such as virtual machinemigration, movement, cloning, check pointing, rollback and/or failoverusing suitable codings of virtual machine state data.

For concreteness, embodiments are described which are based onfacilities, terminology and operations typical of certain processorarchitectures and systems, and based on terminology typical of certainoperating systems, virtualization systems, storage systems and networkprotocols and/or services. That said, the embodiments are general to awide variety of processor and system architectures (including bothsingle and multi-processor architectures based on any of a variety ofinstruction set architectures), to numerous operating systemimplementations and to systems in which both conventional andvirtualized hardware may be provided. As described herein, theembodiments are also general to a variety of storage architectures,including storage virtualization systems such as those based on storagearea network (SAN) or network attached storage (NAS) technologies.

Accordingly, in view of the foregoing and without limitation on therange of underlying processor, hardware or system architectures,operating systems, storages architectures or virtualization techniquesthat may be used in embodiments of the present invention are described.Based on these descriptions, and on the claims that follow, persons ofordinary skill in the art will appreciate a broad range of suitableembodiments.

Computational Systems, Generally

FIG. 20 depicts a collection or cluster of computational systems inwhich an embodiment of the present invention may be used to encode statedata for virtual machines in respective units of a network storage unitssystem and to employ functionality of the network storage system toimplement virtual machine operations that manipulate the respectiveencodings virtual machine state. In particular, FIG. 20 illustrates acollection or cluster in which at least a collection of virtualizationsystems 2012, 2012B, 2012C (but more generally, a mix of virtualizationsystems and conventional hardware systems such as server 2014) areconfigured to share storage resources. In the illustrated collection orcluster, constituent computational systems (e.g., virtualization systems2012, 2012B, 2012C and server 2014) are coupled to network 2020 which isillustrated (for simplicity) as a local area network with client systems2021A, 2021B and communications interface 2022, but will be moregenerally understood to represent any of a variety of networkedinformation systems including configurations coupled to wide areanetworks and/or the Internet using any of a variety of communicationsmedia and protocols.

In the illustrated collection, storage area network (SAN) technology isused for at least some storage needs of computational systemsparticipating in the collection. In general, network storage systems(including SAN-based system 2030) provide a level of virtualization forunderlying physical storage elements (e.g., individual disks, tapesand/or other media), where the characteristics and/or configuration ofparticular storage elements may be hidden from the systems that employthe storage. SAN-based systems typically provide an abstraction ofstorage pools from which individual storage units or volumes may beallocated or provisioned for block level I/O access. In the illustratedcollection, a switched fabric topology consistent with Fibre Channel SANtechnology is shown in which switches 2031A, 2031B, 2031C and/ordirectors are used to mediate high bandwidth access (typically using aSCSI, Small Computer System Interface, command set) to an extensible andpotentially heterogeneous set of storage resources 2032A, 2032B, 2032C,2032D, 2032E, 2032F, 2032G, e.g., SATA (Serial ATA) and/or SCSI disks,tape drives, as well as arrays thereof (e.g., RAID, i.e., RedundantArray of Inexpensive Disks). Such resources may be distributed and (ifdesirable) may provide data replication and/or off-site storageelements. Fibre Channel is a gigabit-speed network technologystandardized in the T11 Technical Committee of the InterNationalCommittee for Information Technology Standards (INCITS).

In general, a variety of different types of interconnect entities,including, without limitation, directors, switches, hubs, routers,gateways, and bridges may be used in topologies (or sub-topologies) thatinclude point-to-point, arbitrated loop, switched fabric portions. FibreChannel and non-Fibre Channel technologies including those based oniSCSI protocols (i.e., SCSI command set over TCP/IP) orATA-over-ethernet (AoE) protocols may be used in embodiments of thepresent invention. Similarly, any of a variety of media including copperpair, optical fiber, etc. may be used in a network storage system suchas SAN 2030.

Although not specifically illustrated in FIG. 20, persons of ordinaryskill in the art will recognize that physical storage is typicallyorganized into storage pools, possibly in the form of RAID groups/sets.Storage pools are then subdivided into storage units (e.g., storagevolumes that are exposed to computer systems, e.g., as a SCSI LUN on aSAN communicating via Fibre Channel, iSCSI, etc.). In some environments,storage pools may be nested in a hierarchy, where pools are divided intosub-pools. In general, persons of ordinary skill in the art willunderstand the SCSI-derived term LUN (Logical Unit Number) to representan address for an individual storage unit, and by extension, anidentifier for a virtual disk of other storage device presented by anetwork storage system such as SAN 2030. By convention, the term LUN isused throughout this description; however, based on the descriptionherein, persons of ordinary skill in the art will appreciate that thisis done without limitation, and that any suitable identifier may beemployed to identify an individual storage unit in embodiments of thepresent invention.

Embodiments of the present invention may be understood in the context ofvirtual machines 2013 (or virtual computers) that are presented oremulated within a virtualization system such as virtualization system2012 executing on underlying hardware facilities 2015. However, inaddition, migration from (or to) a computational system embodied as aconventional hardware-oriented system may be supported in some systemsconfigured in accordance with the present invention. Nonetheless, forsimplicity of description and ease of understanding, embodiments aredescribed in which individual computational systems are embodied asvirtualization systems that support one or more virtual machines.

Although certain virtualization strategies/designs are described herein,virtualization system 2012 is representative of a wide variety ofdesigns and implementations in which underlying hardware resources arepresented to software (typically to operating system software and/orapplications) as virtualized instances of computational systems that mayor may not precisely correspond to the underlying physical hardware.

Overview of Virtualization Systems

The term virtualization system as used herein refers to any one of anindividual computer system with virtual machine managementfunctionality, a virtual machine host, an aggregation of an individualcomputer system with virtual machine management functionality and one ormore virtual machine hosts communicatively coupled with the individualcomputer system, etc. Examples of virtualization systems includecommercial implementations, such as, for example and without limitation,VMware® ESX Server™ (VMware and ESX Server are trademarks of VMware,Inc.), VMware® Server, and VMware® Workstation, available from VMware,Inc., Palo Alto, Calif.; operating systems with virtualization support,such as Microsoft® Virtual Server 2005; and open-source implementationssuch as, for example and without limitation, available from XenSource,Inc.

As is well known in the field of computer science, a virtual machine(VM) is a software abstraction—a “virtualization”—of an actual physicalcomputer system. Some interface is generally provided between the guestsoftware within a VM and the various hardware components and devices inthe underlying hardware platform. This interface—which can generally betermed “virtualization layer”—may include one or more softwarecomponents and/or layers, possibly including one or more of the softwarecomponents known in the field of virtual machine technology as “virtualmachine monitors” (VMMs), “hypervisors,” or virtualization “kernels.”

Because virtualization terminology has evolved over time and has not yetbecome fully standardized, these terms (when used in the art) do notalways provide clear distinctions between the software layers andcomponents to which they refer. For example, the term “hypervisor” isoften used to describe both a VMM and a kernel together, either asseparate but cooperating components or with one or more VMMsincorporated wholly or partially into the kernel itself. However, theterm “hypervisor” is sometimes used instead to mean some variant of aVMM alone, which interfaces with some other software layer(s) orcomponent(s) to support the virtualization. Moreover, in some systems,some virtualization code is included in at least one “superior” VM tofacilitate the operations of other VMs. Furthermore, specific softwaresupport for VMs is sometimes included in the host OS itself.

Embodiments are described and illustrated herein primarily as includingone or more virtual machine monitors that appear as separate entitiesfrom other components of the virtualization software. This paradigm forillustrating virtual machine monitors is only for the sake of simplicityand clarity and by way of illustration. Differing functional boundariesmay be appropriate for differing implementations. In general,functionality and software components/structures described herein can beimplemented in any of a variety of appropriate places within the overallstructure of the virtualization software (or overall softwareenvironment that includes the virtualization software).

Virtual Machine Monitor (VMM)

In view of the above, and without limitation, an interface usuallyexists between a VM and an underlying platform which is responsible forexecuting VM-issued instructions and transferring data to and frommemory and storage devices or underlying hardware. A VMM is usually athin piece of software that runs directly on top of a host, or directlyon the hardware, and virtualizes at least some of the resources of thephysical host machine. The interface exported to the VM is then the sameas the hardware interface of a physical machine. In some cases, theinterface largely corresponds to the architecture, resources and devicecomplements of the underlying physical hardware; however, in other casesit need not.

The VMM usually tracks and either forwards to some form of operatingsystem, or itself schedules and handles, all requests by its VM formachine resources, as well as various faults and interrupts. Aninterrupt handling mechanism is therefore included in the VMM. As iswell known, in the Intel IA-32 (“x86”) architecture, such aninterrupt/exception handling mechanism normally includes an interruptdescriptor table (IDT), or some similar table, which is typically a datastructure that uses information in the interrupt signal to point to anentry address for a set of instructions that are to be executed wheneverthe interrupt/exception occurs. In the Intel IA-64 architecture, theinterrupt table itself contains interrupt handling code and instead oflooking up a target address from the interrupt table, it startsexecution from an offset from the start of the interrupt when a fault orinterrupt occurs. Analogous mechanisms are found in other architectures.Based on the description herein, interrupt handlers may be adapted tocorrespond to any appropriate interrupt/exception handling mechanism.

Although the VM (and thus applications executing in the VM and theirusers) cannot usually detect the presence of the VMM, the VMM and the VMmay be viewed as together forming a single virtual computer. They areshown and described herein as separate components for the sake ofclarity and to emphasize the virtual machine abstraction achieved.However, the boundary between VM and VMM is somewhat arbitrary. Forexample, while various virtualized hardware components such as virtualCPU(s), virtual memory, virtual disks, and virtual device(s) includingvirtual timers are presented as part of a VM for the sake of conceptualsimplicity, in some virtualization system implementations, these“components” are at least partially implemented as constructs oremulations exposed to the VM by the VMM. One advantage of such anarrangement is that the VMM may be set up to expose “generic” devices,which facilitate VM migration and hardware platform-independence. Ingeneral, such functionality may be said to exist in the VM or the VMM.

It is noted that while VMMs have been illustrated as executing onunderlying system hardware, many implementations based on the basicabstraction may be implemented. In particular, some implementations ofVMMs (and associated virtual machines) execute in coordination with akernel that itself executes on underlying system hardware, while otherimplementations are hosted by an operating system executing on theunderlying system hardware and VMMs (and associated virtual machines)executed in coordination with the host operating system. Suchconfigurations, sometimes described as “hosted” and “non-hosted”configurations, are illustrated in FIGS. 9 and 10. However, thedescription herein refers to the physical system that hosts a virtualmachine(s) and supporting components, whether in the “hosted” or“non-hosted” configuration, as a virtual machine host. To avoidconfusion, the “hosted” configuration will be referred to herein as “OShosted” and the “non-hosted” configuration will be referred to as“non-OS hosted.” In the “OS hosted” configuration, an existing,general-purpose operating system (OS) acts as a “host” operating systemthat is used to perform certain I/O operations. In the “non-OS hosted”configuration, a kernel customized to support virtual machines takes theplace of the conventional operating system.

OS Hosted Virtual Computers

FIG. 9 depicts an embodiment of a virtualization system configurationreferred to as an “OS hosted” configuration. Virtualization system 900includes virtual machines 950, 950A, and 950B and respective virtualmachine monitors VMM 910, VMM 910A, and VMM 910B. Virtualization system900 also includes virtualization layer 990, which includes VMMs 910,910A, and 910B. VMMs 910, 910A, and 910B are co-resident at system levelwith host operating system 920 such that VMMs 910, 910A, and 910B andhost operating system 920 can independently modify the state of the hostprocessor. VMMs call into the host operating system via driver 921 and adedicated one of user-level applications 930 to have host OS 920 performcertain I/O operations on behalf of a corresponding VM. Virtual machines950, 950A, and 950B in this configuration are thus hosted in that theyrun in coordination with host operating system 920. Virtual machine 950is depicted as including application guests 961, operating system guest951, and virtual system 952. Virtualization systems that includesuitable facilities are available in the marketplace. For example,VMware® Server virtual infrastructure software available from VMware,Inc., Palo Alto, Calif. implements an OS hosted virtualization systemconfiguration consistent with the illustration of FIG. 9; and VMware®Workstation desktop virtualization software, also available from VMware,Inc. also implements a hosted virtualization system configurationconsistent with the illustration of FIG. 9.

Non-OS Hosted Virtual Computers

FIG. 10 depicts an embodiment of a virtualization system configurationreferred to as a “non-OS hosted” virtual machine configuration. In FIG.10, virtualization system 1000 includes virtual machines 950, 950A, and950B as in FIG. 9. In contrast to FIG. 9, virtualization layer 1092 ofFIG. 10 includes VMMs 1010, 1010A, and 1010B, and dedicated kernel 1090.Dedicated kernel 1090 takes the place, and performs the conventionalfunctions, of a host operating system. Virtual computers (e.g., VM/VMMpairs) run on kernel 1090. Virtualization systems that include suitablekernels are available in the marketplace. For example, ESX Server™virtual infrastructure software available from VMware, Inc., Palo Alto,Calif. implements a non-hosted virtualization system configurationconsistent with the illustration of FIG. 10.

Different systems may implement virtualization to differentdegrees—“virtualization” generally relates to a spectrum of definitionsrather than to a bright line, and often reflects a design choice inrespect to a trade-off between speed and efficiency and isolation anduniversality. For example, “full virtualization” is sometimes used todenote a system in which no software components of any form are includedin the guest other than those that would be found in a non-virtualizedcomputer; thus, the OS guest could be an off-the-shelf, commerciallyavailable OS with no components included specifically to support use ina virtualized environment.

Para-Virtualization

Another term, which has yet to achieve a universally accepteddefinition, is “para-virtualization.” As the term implies, a“para-virtualized” system is not “fully” virtualized, but rather a guestis configured in some way to provide certain features that facilitatevirtualization. For example, the guest in some para-virtualized systemsis designed to avoid hard-to-virtualize operations and configurations,such as by avoiding certain privileged instructions, certain memoryaddress ranges, etc. As another example, many para-virtualized systemsinclude an interface within the guest that enables explicit calls toother components of the virtualization software. For some, the termpara-virtualization implies that the OS guest (in particular, itskernel) is specifically designed to support such an interface. Accordingto this definition, having, for example, an off-the-shelf version ofMicrosoft Windows XP as the OS guest would not be consistent with thenotion of para-virtualization. Others define the termpara-virtualization more broadly to include any OS guest with any codethat is specifically intended to provide information directly to theother virtualization software. According to this definition, loading amodule such as a driver designed to communicate with othervirtualization components renders the system para-virtualized, even ifthe OS guest as such is an off-the-shelf, commercially available OS notspecifically designed to support a virtualized computer system.

Unless otherwise indicated or apparent, virtualized systems herein arenot restricted to use in systems with any particular “degree” ofvirtualization and are not to be limited to any particular notion offull or partial (“para-”) virtualization.

Provisioning in a Virtualization System Supported with Network Storage

Provisioning Integration

Network storage systems provide virtualized storage where the physicalstructure of the storage (e.g., individual disks, tapes or other media)is hidden from the user. Network storage systems provide abstractions ofstorage pools and/or storage units to manage the physical storage. Forexample, physical storage is often organized into storage pools,possibly in the form of RAID groups/sets. Storage pools can then besubdivided into storage units, which are then exposed to computersystems (e.g., a SCSI LUN on a SAN communicating via Fibre Channel,iSCSI, etc.). In some environments, storage pools may be nested in ahierarchy, where pools are divided into sub-pools.

FIG. 1A depicts an example of a system that incorporates network storagesystem capabilities into virtual machine provisioning. For purposes ofillustration, the system includes a SAN-type implementation of thenetwork storage although, based on the description herein, persons ofordinary skill will appreciate other implementations including, withoutlimitation, NAS-type and other storage systems that provide volumemanagement features. In FIG. 1A, a network storage system includes rawstorage devices 115A-115F and 116A-116F (e.g., disks, tapes, etc.). Thenetwork storage system also includes network storage communicationsmedium 107. Network storage communications medium 107 may be realizedwith a variety of technologies (e.g., Fibre Channel, dark fiber, IP overGigabit Ethernet, ATA over Ethernet (AoE), SONET, ATM, etc.). Inaddition, the network storage communications medium 107 may also includeone or more of a router, switch, etc. Raw storage devices 115A-115F and116A-116F are logically organized into storage pools 121A-121C. Virtualmachine management system 101 allocates network storage unit 109 fromstorage pool 121A for a first virtual machine 102A. Virtual machinemanagement system 101 also allocates network storage unit 111 fromstorage pool 121A for second virtual machine 104A and network storageunit 112 for third virtual machine 104B. Allocation of a storage unitmay involve both creation of a network storage unit and designation ofthe network storage unit for a virtual machine or designation of analready created network storage unit for a virtual machine. Virtualmachine management system 101 communicates with virtualization systems105 and 103 via network 117.

In the illustrated configuration, virtualization system 105 supportsvirtual machines 102A-102B, and virtualization system 103 supportsvirtual machines 104A-104B. Although virtual machines 102A and 104A aredepicted in FIG. 1A on separate virtualization system, embodiments arenot so limited. A virtualization system may support larger or smallernumbers of virtual machines, and may support different numbers ofvirtual machines at different times. Virtual machine management system101 indicates to virtualization system 105 that network storage unit 109has been allocated for a virtual machine of virtualization system 105.Likewise, virtual machine management system 101 indicates tovirtualization system 103 that network storage units 111 and 112 havebeen allocated for virtual machines 104A and 104B.

Storage abstractions provided by network storage systems can be directlyused by the virtual machine management system to integrate virtualmachine provisioning and storage provisioning. For example, one or morestorage pools may be assigned to a virtual machine manager. A virtualmachine provisioning operation will automatically provision storageunits from the assigned storage pools. The degree of exposure of anetwork storage system to virtual machine management may vary based onneeds/structure of a particular entity. The degree of integration offacilities of a network storage system and a virtualization system willvary in accordance with the degree of exposure. A small entity, forexample, may wish to task a single group with management of bothvirtualization systems and storage systems. Full exposure of the rawstorage devices can allow for full integration of virtualizationmanagement and storage management. Full exposure of raw storage devicesto a virtualization management system allows the virtualizationmanagement system to organize the raw storage devices into logicalunits. In such a scenario, the virtualization management system maycreate the abstraction of storage units directly upon the raw storagedevices, or create additional layers of abstraction, such as storagepools.

In another scenario, an entity may outsource management of storagedevices or utilize a third-party vendor that provides access to rawstorage devices while managed by the third party vendor allowing theentity to retain some degree of control of the raw storage devices. Inthis third-party scenario, the entity responsible for management of theraw storage devices may expose storage pools to the entity managingvirtual machines. Hence, the raw source devices are hidden from thevirtual machine management entity, but are provided some latitude inmanagement of the storage. This allows the virtual machine managemententity greater ability to tailor the storage to their needs.

A large entity may have an established division for management of theirstorage devices separate from a division for virtualization. Such alarge entity may wish to maintain distinct separation between thedivisions. Hence, the virtualization division would only have exposureto units of the network storage as allocated by the storage devicedivision, perhaps as requested by the virtualization division. However,as already stated, some degree of integration of network storagemanagement and virtual machine management satisfies some calls forefficiency.

FIG. 2 depicts a flowchart of an embodiment for partial integration ofvirtual machine provisioning and network storage provisioning. At block201, available storage pools are discovered. Discovery may involvedetermining identifying information, total capacity information, etc.Various techniques can be utilized to implement storage pool discovery(e.g., masking). A virtual machine management system may be limited todiscovering only those storage pools elected to be exposed by a remotestorage management system. A remote management system may elect toexpose all storage pools that have been created, or limit exposure toparticular storage pools in accordance with certain variables (e.g.,location of the raw storage devices, percentage of storage pools,storage pools currently used by virtualization systems, etc.).

At block 202, the storage pool is selected. At block 203, networkstorage units are created in the selected storage pool. The networkstorage units are created in accordance with configuration settings thatindicate, for example, a given size for each network storage unit. Thesize may be a default size, a discrete size selected from multipleoptions, user defined size, etc. At block 205, the created networkstorage units are designated for virtual machine data. A virtual machinemanager may mark each of the created network storage units with a valueidentifying the network storage units as supporting virtual machines.Marking may be implemented by writing a partition type into a rootpartition for a network storage unit that has been associated withvirtual machines. However, it is possible that a partition type may beoverloaded with multiple associations. In addition to, or instead of,partition type marking, a unique value may be written into the networkstorage unit. For example, a checksum may be coded into the virtualmachine data stored in a network storage unit. A discovery operationwould then search for both the partition type and the checksum to verifythat the network storage unit has been designated for virtual machines.Indication of whether a network storage unit supports a virtual machinemay be maintained in a data structure separate and distinct from thenetwork storage units in addition to or instead of marking the creatednetwork storage units.

To help illustrate, the following example configuration is provided,which refers to an industry standard Storage Management InitiativeSpecification (SMI-S). Storage array vendors typically provide APIs forthird party management. One example is the industry standard SMI-S,which describes vendor neutral interfaces to manage storage arrays. Avirtual machine manager may configure storage (i.e., provision logicalrepresentations of raw storage) for virtual machine provisioningautomatically or manually. If automatic configuration is implemented,then the virtual machine manager performs Service Location Protocol(SLP) discovery for SNIA SMI-S registered profiles. The virtual machinemanager displays a list of discovered network storage in auser-interface and prompts a user to enter a user/password. After theuser enters a valid name/password for the discovered network storage,the virtual machine manager authenticates. If manual configuration isimplemented, a user enters an IP address (optional port number) andname/password for the network storage management interface. With theentered information, the virtual machine manager authenticates. Afterauthenticating, the virtual machine manager connects to the networkstorage unit and discovers available storage pools. From the availablediscovered storage pools, the virtual machine manager divides the poolsinto primordial pools and data store pools, from which network storageunits are created. The virtual machine manager enumerates units (e.g.,logical unit numbers (LUNs)) of the network storage from the storagepools, and compares the enumerated units against a list of in-banddiscovered LUNs across applicable hosts. The virtual machine managerdisplays root/boot LUNs, known virtual machine LUNs, and all other LUNsseparately.

Referring again to FIG. 2, at block 209, a unit of network storagedesignated for support of a given virtual machine is communicated to acorresponding virtualization system. For example, a virtual machinemanager identifying information for a network storage unit communicateswith a virtualization layer on the virtualization system. Thevirtualization layer may then map the identified network storage unit toa host bus adapter exposed by the virtualization system to thecorresponding virtual machine.

Of course, creation and designation of network storage units for virtualmachines does not necessitate immediate or contemporaneous creation of avirtual machine or communication of a network storage unit to thevirtualization system. In general, the division of labor between avirtual machine manager and a virtualization layer of a virtualizationsystem represents an implementation choice and implementations can varygreatly. For example, a virtual machine manager may only perform storagepool discovery and communicate discovered storage pools to thevirtualization layer of a virtualization system. The virtualizationlayer may be responsible for creation of network storage units,designation of the created network storage units for virtual machines,and eventual provisioning of a virtual machine. In another example, avirtual machine manager may perform all operations from storage unitdiscovery (perhaps even storage unit creation), to provisioning andactivation of a virtual machine. In this embodiment, a virtualizationlayer is tasked with the responsibility of operating and exposingresources to supported virtual machines executing in coordinationtherewith. Regardless of the division of labor in a particularembodiment, provisioning of a virtual machine involves preparation of acorresponding network storage unit. Preparation involves formatting of anetwork storage unit, and possibly initialization of the network storageunit with certain data for a virtual machine. Preparation of networkstorage unit may be entirely performed by a virtual machine manager or avirtualization layer, collectively performed by a virtual machinemanager and a virtualization layer, alternately performed, etc.

Mutually Exclusive Network Storage Units for Individual Virtual Machines

FIG. 1B depicts preparation of allocated network storage units in thesystem of FIG. 1A. In FIG. 1B, virtualization system 105 communicateswith the network storage system via network storage communicationsmedium 107. Virtualization system 105 communicates with the networkstorage system to prepare network storage unit 109 to support a singlevirtual machine. Although the description refers to interactions withnetwork storage units, it should be understood that the units arelogical representations and that the interactions are actually with theunderlying hardware. Virtualization system 103 prepares separate networkstorage units 111 and 112 of the network storage system to supportrespective virtual machines 104A and 104B, which will be executed incoordination with virtualization system 103. The state data, and perhapsother data, of individual virtual machines 102A, 104A, and 104B, are notcommingled in network storage units 109, 111, and 112. Preparation of ashared storage unit to support a virtual machine may involve formatting,initialization, encryption, etc. Although FIG. 1B depicts thevirtualization system preparing units of network storage, a portion orall of the preparation functionality may be performed by a virtualmachine manager as stated above.

Although the above depicts allocation and preparation of a single unitof network storage for each virtual machine, multiple units of networkstorage may be allocated and prepared for a given virtual machine.Virtual machine provisioning can range from completely encapsulating asingle virtual machine in a single network storage unit (i.e., storingstate data, virtual primary disk data, virtual hardware configurationdata, snapshot data, virtual secondary disk data, etc.) to allocatingindividual network storage units for each aspect of a virtual machine(e.g., a network storage unit for each of virtual hardware configurationdata, state data, virtual primary disk data, boot sector, etc.). Inlight of these variations, the network storage unit that backs statedata of a virtual machine is referred to herein as the base unit,whether or not the unit also encodes additional data.

FIG. 3 depicts a flowchart of an embodiment for allocation of multipleunits of network storage for a virtual machine. At block 301, networkstorage units available for virtual machines are discovered. At block303, a network storage unit is selected as a base unit for a virtualmachine. At block 307, the base unit is mapped to a virtualizationsystem. At block 309, it is determined whether secondary virtual disksare to be provisioned for the virtual machine. If secondary virtualdisks are to be provisioned, then control flows to block 311. Ifsecondary virtual disks are not to be provisioned, then control flows toblock 317.

At block 311, one or more additional units of network storage areallocated for one or more secondary virtual disks. At block 313, theadditional network storage units for the secondary disks are indicated.Various techniques can be utilized to indicate the additional units ofnetwork storage allocated for the virtual secondary disks of the virtualmachine. For example, indications may be written into the base unit toidentify the additionally allocated units of network storage as virtualsecondary disks (e.g., the base unit will identify a globally unique ID,such as SCSI Inquiry VPD page 0x83, for a secondary virtual disk). Theglobally unique ID will allow the virtual secondary disks to beautomatically detected and attached to the virtual machine. Theindications of the additional network storage units as virtual secondarydisks may alternatively, or in addition, be communicated to thevirtualization system. The secondary virtual disk network storage unitsmay also be marked to distinguish them from base units. Control flowsfrom block 313 to block 317. At block 317, the base unit is indicated tothe virtualization system at least for backing state data of the virtualmachine.

For a given embodiment, the degree of separation of virtual machinesacross network storage units can range from only separating state datafor virtual machines to separating all data for virtual machines. Forexample, a first network storage unit may encode a library of possiblevirtual hardware configuration. While the state data of two distinctvirtual machines would be backed on separate network storage units,these two distinct virtual machines may point to the same or differentvirtual hardware configuration data in the library. In another example,two distinct virtual machines may share a virtual secondary disk on anetwork storage unit while their respective virtual primary disks andstate data are stored on mutually exclusive network storage units.

In general, prevention of commingling of state data of the state virtualmachines may be enforced implicitly or explicitly. For example, anembodiment of a virtual machine manager may not present a networkstorage unit already encoding state data of a virtual machine duringvirtual machine provisioning. However, in some cases, a given embodimentof a virtual machine manager may preserve the availability forprovisioning multiple virtual machines onto a single network storageunit, perhaps for performance comparison purposes, dwindling resources,etc. Of course, the preserved option would involve mounting a filesystem as intermediary between a virtual machine and a network storagesystem, thus losing integration of the virtualization system in thenetwork storage system and manageability of virtual machines at networkstorage unit granularity.

As mentioned above, data that encodes a virtual machine typicallyincludes multiple data components: state data, virtual primary disk(sometimes referred to as virtual primary disk data), virtual hardwareconfiguration data (e.g., type of processor, type of virtual networkcard, type of virtual storage host bus adapter (HBA), amount of memory,etc.), snapshot data, and zero or more virtual secondary disks(sometimes referred to as virtual secondary disk data). Those ofordinary skill in the art should appreciate that in various embodimentsthese multiple data components may be aggregated together, separateddifferently across different embodiments, further divided, etc. Thestate data of a virtual machine indicates execution state of a virtualmachine at a particular time whether suspended or not suspended. Forexample, state data indicates current data in all or a portion of amemory of a virtual machine (e.g., instruction and/or value data in thevirtual machine's RAM, cache, registers, etc.). A boot disk (e.g., aboot sector and OS disk image) may reside on the primary virtual disk,virtual secondary disks, or not be present at all for “network boot” ofvirtual machines. Virtual hardware configuration data indicates aconfiguration of a virtual machine. For example, virtual hardwareconfiguration data indicates a type of virtual processor, type ofvirtual network card, type of virtual storage HBA, amount of virtualRAM, virtual chipset, type and size of a virtual primary disk, etc.

FIG. 4 depicts an organization of network storage unit 400 that onlyencodes state data for a single virtual machine. FIG. 5 depicts anorganization of network storage unit 500 that encodes virtual machinedata with the exception of a virtual primary disk. Network storage unit500 has been prepared to encode, or currently encodes, state data,virtual hardware configuration data, and snapshot data for a virtualmachine. A root partition table has been written into network storageunit 500 to indicate individual partitions for each of the encoded datacomponents. Presumably, virtual primary disk data is encoded on anothernetwork storage unit. It should be understood that the order of dataillustrated in FIGS. 5, 6 and 7 is for illustrative purposes alone, andis not meant to be limiting. A network storage unit can be organized ina number of different ways.

FIG. 6 depicts an organization of network storage unit 600 that encodesvirtual machine data including a virtual primary disk. Network storageunit 600 has been prepared to encode, or currently encodes, a virtualprimary disk, state data, virtual hardware configuration data, andsnapshot data for a virtual machine. A root partition table has beenwritten into network storage unit 600 to indicate individual partitionsfor each component of the encoded data. If there are any virtualsecondary disks for the virtual machine, they are implemented with aseparate network storage unit.

The virtual machine manager or virtualization layer of the correspondingvirtualization system should allocate enough space in the state dataportion of a network storage unit to support the configured memory sizeof the virtual machine. To support memory growth in the future, thevirtual machine manager or virtualization layer (provisioningfunctionality) may choose to over-allocate space to accommodate thegrowth. The provisioning functionality may later change a virtual disksize or the supported virtual RAM size by extending the unit of networkstorage, updating a top-level partition data structure, and moving thedata around (e.g., to the end of the network storage unit in the datastructure outlined above). If the virtual disk size is being expanded,the virtual disk exposed to a guest will now report a larger size. IfRAM is being added, the state data region will be increased. The statedata region and other regions are typically small compared to virtualdisks, so this reconfiguration should be a relatively fast operation.The provisioning computation may also choose to use a fragmented modelwithout relocating regions when growing/shrinking the network storageunit.

FIG. 7 depicts an organization of network storage unit 700 that encodesvirtual machine data including multiple virtual disks. Network storageunit 700 has been prepared to encode, or currently encodes, a virtualprimary disk, a virtual secondary disk, state data, virtual hardwareconfiguration data, and snapshot data for a virtual machine. A rootpartition table has been written into the network storage unit toindicate individual partitions for each of the virtual machine datacomponents. The virtualization layer on a virtualization system canexamine the root partition table to read and write to the variouspartitions. The state data for the virtual machine is written directlyinto the state data partition. On boot, the virtual machine gets accessto the entire network storage unit and sees its virtual primary disk(typically with the installed operating system) and virtual secondarydisk, and ignores the other data partitions.

Regardless of the particular embodiment, allocating mutually exclusivenetwork storage units for distinct virtual machines dispenses with atraditional file system to store data components of the virtual machine.Dispensing with the traditional file system allows, for example, astorage virtualization engine to communicate directly with a networkstorage unit manager (assuming a virtual machine stack that comprises avirtual machine, a storage virtualization engine (i.e., instantiatedcode that presents virtual storage to a virtual machine), a networkstorage manager (e.g., a SAN agent), and a communication mediuminterface). The intermediary file system that would reside between thestorage virtualization engine and the network storage manager has beenobviated. With at least mutually exclusive network storage units backingstate data of a virtual machine, the entire virtual machine state isencapsulated in a single base unit.

Securing Virtual Machine Data

Since a virtual machine has complete access to an entire network storageunit, a guest may also have access to the entire network storage unit.It would be prudent to restrict access to non-disk data. Exposing thestate data, virtual hardware configuration data, or snapshot data canpotentially leak sensitive information to a guest of the virtualmachine. Actions by a guest, whether accidental or intentional, couldresult in the deletion or corruption of this data. Restricting guestaccess to non-disk data provides security and reliability. Furthermore,the potential harmful and/or undesirable exposure of non-disk data to aguest of a virtual machine is not limited to virtual machines with datastored in remote shared storage. For example, risks may also exist for avirtual machine with data stored in remote unshared storage, storagelocal to the hardware system that supports a given virtual machine(e.g., flash memory plugged into a USB port, a local disk, etc.).

To address this concern, non-disk data is isolated from disk data. Amethod for isolating disk data from non-disk data would be to limitguest access to a partition of a network storage unit that encodes avirtual primary disk, and zero or more partitions that encode virtualsecondary disks. For example, the virtualization layer on avirtualization system, perhaps a virtual machine monitor in thevirtualization layer, provides a virtualized SCSI disk to the virtualmachine that only includes a virtual disk partition. To the virtualmachine, this looks like a regular virtual disk with its own partitiontable and partitions. A guest of the virtual machine is no longer ableto access the non-disk data.

FIG. 8A depicts a virtualization system securing non-disk data. In FIG.8A, virtual machine management system 801 formats network storage unit811 of storage pool 815 to at least secure state data, if not allnon-disk data of the virtual machine. Virtual machine management system801 formats network storage unit 811 via communications medium 807.

FIG. 8B depicts an organization of an encoding (in a unit of networkstorage 800) of virtual machine data. The encoding seeks to isolate andto secure non-disk data. In the illustrated encoding, a pair of nestedpartition tables has been written: a root partition for the entirenetwork storage unit, and a second partition table for the primaryvirtual disk partition. In the illustrated encoding, the primary virtualdisk partition has also been further partitioned. By nesting partitions,the illustrated encoding allows a virtualization system to expose onlycontents of the primary virtual disk to the corresponding virtualmachine and any guest operating system/applications executing thereon.

Referring again to FIG. 8A, after formatting network storage unit 811,virtual machine management system 801 communicates informationconcerning the primary virtual disk partition to the virtualizationlayer of virtualization system 805, which in turn exposes only thevirtual disk data.

Although the embodiment(s) described with reference to FIGS. 8A and 8Bemploys a unit of network storage, further embodiments of the inventivetechniques can more generally be applied to other types of storage. Forexample, a local storage may be partitioned into multiple partitions. Atleast two partitions are allocated to a virtual machine, but a guest ofthe virtual machine is restricted to accessing the one or morepartitions that encode disk data. The local storage may be organized inaccordance with a file system. Different permission levels are assignedto folders. A folder that includes disk data for various virtualmachines is set with a lower level permission than is granted to guests.A different folder that includes non-disk data is set with a privilegedpermission level granted to the virtualization layer, but not granted toguests. Permission levels may be applied to individual files in additionto setting access permissions for folders or instead of settingpermission for folders.

Another method for restricting access to non-disk data hides thenon-disk data from a guest while exposing a global partition table. Forexample, the non-disk data, whether or not organized into differentpartitions, are located at a location in a partition or storage known tothe virtualization layer. The size of the storage, folder, or partition,is truncated when reported to a guest to hide the region occupied bynon-disk data. Hiding the region occupied by non-disk data obviatesmodification of I/O requests with offsets.

Methods that align the beginning of a virtual disk with the beginning ofa physical storage for a virtual machine can also be used to concealnon-disk data from a guest. A partition table for the virtual disk isstored in a non-disk data partition. When a guest requests access to thebeginning of the storage, the second partition table is fetched andexposed to the guest. Attempted access by the guest to other than thebeginning of the storage is allowed if not off the truncated end.

Operations of Virtual Machine Directly Supported by Network Storage

Access Requests from a Virtual Machine Guest

As described above, in some embodiments of the present invention, avirtual machine directly accesses data encoded in a unit of networkstorage rather than via an intermediate file system interface. Toenforce security and restrict access by a guest of a virtual machine toat least state data, if not all non-disk data, the virtualization layerintercepts requests from a guest of a virtual machine.

FIG. 11 depicts an embodiment of a virtualization layer interceptingdisk access requests from a guest of a virtual machine. In FIG. 11,virtualization system 1100 includes virtual machine 1150, virtualizationlayer 1192, and underlying system hardware 920. Application guest 1161executing in virtual machine 1150 initiates a disk access request. Thedisk access request traverses operating system guest 1151 and virtualsystem 1152. Virtualization layer disk I/O handler 1194 receives thedisk access request. Virtualization layer disk I/O handler 1194 modifiesan indication of the location to be accessed. For example, in somerealizations, an offset is added to appropriately align the accessrequest in the virtual disk partition of a network storage unit thatencodes the virtual disk. The modified access request is then passed tonetwork storage management agent 1196 (e.g., the modified access requestis passed to an I/O interface for network storage). The virtualizationlayer (e.g., the disk I/O handler) may perform additional operations toprevent access to non-disk data by a guest. For example, thevirtualization layer may verify that a modified location indicationfalls within boundaries designated for access requests destined for anetwork storage unit. If a modified location indication falls within theboundaries, then the corresponding access request is valid and isallowed to proceed. Otherwise, the guest is notified that the accessrequest failed or has been denied. Network storage management agent 1196generates a corresponding network storage unit access request (e.g., I/Ocommand). The network storage access request is then passed tounderlying system hardware 920. From system hardware 920, the accessrequest is transmitted to the network storage unit that encodes thevirtual machine's virtual disk.

For a response to an access request, the reverse of the operationsdepicted in FIG. 11 are applied. A response received by system hardware920 would be passed to virtualization layer 1192. In virtualizationlayer 1192, the network storage management agent 1196 extracts a payloadfrom the response and passes the payload (e.g., read request data) tothe virtualization layer disk I/O handler 1194. The virtualization layerdisk I/O handler 1194 then modifies any location indication to concealnon-disk data locations from the application guest 1161 (e.g., subtractsan offset) and, perhaps, the operating system guest 1151. Thevirtualization layer disk I/O handler 1194 passes the response with themodified location indication to the virtual system 1152. The applicationguest 1161 eventually receives the response to its initiated disk accessrequest with the modified location indication. Although the abovedescribes an embodiment for preventing access to certain, if not all,non-disk data by a guest of a virtual machine, the scope of restrictionmay be expanded to include the virtual machine data. In general, accessto non-disk virtual machine data may be limited to a virtualizationlayer that supports the corresponding virtual machine.

As previously stated, other techniques for concealing non-disk data froma guest may be implemented that avoid modifying requests with an offset.For example, storage size may be truncated when reported to a guest toconceal a region occupied by non-disk data. The previously describedalignment technique also avoids modifying access requests from guestswith offsets. Avoiding offset modification can be implemented with aless performance intensive set of operations (e.g., introducing acompare operation and a branch predict operation to the I/O path insteadof a set of operations to compute and apply an offset).

Exposing Non-Disk Data Locations in a Network Storage Unit for Backupand Snapshot

Although non-disk data locations of the network storage unit are hiddenfrom guests of a virtual machine, non-disk data locations are exposed toa corresponding virtualization system for certain management operations,such as backup operations and snapshot operations. A component of avirtualization layer (e.g., a network storage management agent) hasdirect access to a network storage unit. Direct access to a networkstorage unit allows state data to be written directly to a backingnetwork storage unit for efficient backup of the state data. It is notnecessary, however, for functionality that performs a write for backingstate data to be resident in the virtualization layer or embodied as aseparate agent. Embodiments may implement the backup writingfunctionality in the virtual system exposed to a virtual machine, in anagent that is separate from the virtual machine and the virtualizationlayer, etc.

Similarly, snapshot functionality may be implemented in the exposedvirtual system, in the virtualization layer, in a separate agent, as anagent in the virtualization layer, etc. Regardless of the particularimplementation, by exploiting direct access to a network storage systemand an n:1 relationship between network storage units and virtualmachines, a virtualization system can leverage facilities of a networkstorage system. In general, a network storage system applicationprogramming interface allows direct access by a virtualization system tosnapshot facilities of a network storage management system. Allocationof mutually exclusive network storage units for distinct virtualmachines allows one to use network storage management system facilitieswithout the overhead from an intermediary file system.

Modern storage arrays typically provide the ability to snapshot astorage volume. A snapshot is typically implemented as copy-on-writeimplemented at the storage array layer where a second volume is createdand linked to the first volume. To the client of the array, a snapshotresults in a second volume that has the exact state of the originalvolume at the point the snapshot was taken. Arrays provide furthercapabilities such as refreshing a snapshot to bring it back intosynchronization with the base volume, as well as severing a link betweenthe two volumes to make clones. Since state data for a single virtualmachine is completely stored in a base network storage unit, taking asnapshot for a virtual machine can be implemented with a write operationto the base unit and a network storage management system snapshotoperation of the base unit, and, perhaps, any supplemental networkstorage units for the virtual machine.

FIG. 12 depicts an embodiment of snapshot operations for a virtualmachine. At the virtualization layer of a virtual machine, snapshottingis activated. This may be done using a variety of trigger mechanisms.For example, snapshotting may be activated by a manual event, a timebased event, in accordance with a configuration file, a notification orcommand received via a communications medium, etc. Next, the snapshotactivation causes a snapshot network storage unit to be linked to a basenetwork storage unit that encodes at least state data of the virtualmachine. Next, the snapshot network storage unit is identified to thevirtualization layer. Next, the virtualization layer indicates theidentity of the base unit in the state data portion (or some otherportion, such as the virtual hardware configuration data portion) of thesnapshot network storage unit. Next, local snapshot operations are thentriggered. The virtualization layer marks pages of the state data ascopy-on-write. Upon writing to one of these pages, the virtualizationlayer pages out state data. The state data is written to the base unit.The virtualization layer also causes I/O to be flushed out to theprimary virtual disk, which in this example is in the base networkstorage unit.

Once this point is reached where a consistent state can be conveyed forthe virtual machine, the virtualization layer triggers a snapshot of thebase network storage unit to the linked snapshot network storage unit.This causes the underlying facilities of the network storage (e.g.,network storage management system) to copy the data of the base networkstorage unit and store it as “snapshot 1” in the snapshot networkstorage unit. The virtualization also begins routing I/O to the snapshotnetwork storage unit, which is written as current state data for thevirtual machine. This process repeats as long as snapshot activationcontinues, storing a given number of snapshots in a different networkstorage unit.

FIG. 12 further depicts subsequent snapshots (i.e., snapshot children)being stored in the same network storage unit as the parent snapshot. Ofcourse, the parent snapshot may only include a delta of the data storedin the base network storage unit. In the illustrated embodiment ofstoring children in the same network storage unit as the parentsnapshot, the next trigger of local snapshot operations again causespages to be marked as copy-on-write. State data is paged out to thesnapshot network storage unit. The I/O is flushed out to disk on thesnapshot network storage unit. The trigger of network storage snapshotdoes not make a copy, but stores the data that has been paged out andflushed out as “snapshot 2.” As already stated, embodiments can beenvisioned that store snapshots in different network storage units, inthe base network storage unit, etc.

In the context of arrays and volumes, the VM snapshot is now stored in aseparate volume (or volumes if multiple disks are in use by the VM).Multiple VM snapshots can be supported by performing multiple snapshotson the array. In the state data portion of the base volume, referencescan be stored to the snapshot parent base volume, so the virtual machinemanager can discover the parent child relationship between snapshots. Inthis approach, the copy-on-write is not implemented in the virtualmachine or in a file system layer, but in the storage array layer.

Typically, storage arrays change the unique ID of the snapped volume todistinguish it from the base volume. Many operating systems, especiallythose with advanced multipath capabilities, use the unique ID of avolume as the ID for their disks instead of relying on the SCSI targetand unit numbers. In a virtualization environment, the same ID for thevirtual disk can be exposed to a guest(s) of a virtual machine;otherwise, drivers within an OS guest may become confused and may crashthe OS. Within the state data portion of the base disk, or even aseparate location, the “initial” unique ID for the volume(s) isrecorded. When using snapped volumes, the virtualization layer willinterpose and replace the snapped ID with the initial ID so that the OSguest is unaware that it is operating on a snapshot. Of course, thisfunctionality is not limited to snapshotting the state data. A snapshotmay be taken of the entire base unit, a very active portion of the statedata (assuming there is a very active and less active state dataportions), the primary virtual disk and state data, all disks and statedata, etc.

Although an initial snapshot includes all data (e.g., all state data,all data in a base unit, etc.), subsequent snapshots may be taken inaccordance with a variety of snapshotting techniques. For example, eachsnapshot in a series of snapshots may include all data at the particularmoment of the snapshot, or only the difference between the currentsnapshot and a predecessor snapshot, which is not necessarily the rootsnapshot or immediately preceding snapshot. For example, a snapshot xmay only include differences between itself and snapshot x−3. Thesnapshot may include a reference to the snapshot x−3, which may includeanother reference to the base snapshot. Another approach may tracksnapshot relationships in a table, linked list, etc. Those of ordinaryskill in the art should appreciate that a variety of data structures maybe utilized to encode snapshots and/or snapshot relationships.

FIG. 13 depicts a flowchart of an embodiment of a method for activatinga snapshot. At block 1301, a snapshot of a virtual machine is selected.At block 1303, it is determined whether the virtual machine is running.If the virtual machine is running, then control flows to block 1305. Ifthe virtual machine is not running, then control flows to block 1307.

At block 1305, the virtual machine is stopped. Although the virtualmachine is stopped in the illustrated embodiment, embodiments inaccordance with the present invention may suspend the virtual machine,thus preserving running state if so desired. In either case, the virtualmachine state (in network storage) will be consistent and suitable forsnapshot. At block 1307, the selected snapshot data is loaded from thecorresponding network storage unit. At block 1309, it is determinedwhether additional corresponding snapshot data resides on other networkstorage units (e.g., snapshots of virtual secondary disks thatcorrespond to the selected snapshot). If additional snapshots exist,then control flows to block 1311. If there are no other correspondingsnapshots for the virtual machine, then control flows to block 1313. Atblock 1311, the corresponding snapshots in the other network storageunits are bound to the selected snapshot. At block 1313, the virtualmachine is resumed with the selected snapshot.

Maintaining snapshots of virtual machines allows activation of a virtualmachine(s) at different points in time, which can be used for a myriadof purposes such as testing, agent-less back-up, offline virus scanningand other integrity checks, etc. When reverting to a previous snapshot,it may be desirable to discard an intermediate snapshot and maintain asnapshot that reflects a most recent state. For example, a snapshot tobe deleted may correspond to state results from a failed test orexperiment. This can also be used for applications that reset and eraseany changes made by users upon every reboot, such as a kioskapplication. Discarding or deleting the intermediate snapshot may reducecomplexity and possibly improve performance. In a snapshot hierarchythat maintains children snapshots with deltas, a to-be-deleted snapshotmay be rolled back into the predecessor intermediate snapshot, thuseffectively deleting the intermediate snapshot. Of course, the snapshotto be discarded is not necessarily an intermediate snapshot, and may bethe most recent snapshot. Those of ordinary skill in the art shouldappreciate the availability of methods for deleting a child snapshot.

Virtual Machine Management with Network Storage Facilities

In addition to the ability to snapshot, virtual machine management mayinclude functionality to clone and/or migrate virtual machines (runningor offline). These functions are typically implemented using redo-logswith copy-on-write semantics. With a network storage unit devoted to asingle virtual machine, redo logs have been discarded along with theindependent intermediary file system. With access to built-in facilitiesof a network storage system, virtual machine management can leverage thenetwork storage management operations to efficiently manage virtualmachines (e.g., clone, migrate, discovery, replicate for disasterrecovery, etc.). The facilities are exposed to a virtualization systemwith an application programming interface for network storage management(“storage API”) and exposure of network storage units. The functionalitythat makes calls to the storage API may be implemented as part of avirtual machine manager that resides on a server communicatively coupledto virtualization system, part of a virtual machine manager that resideson a virtualization system, etc.

Discovery

Instead of initiating a communication session with every virtualizationsystem, or accessing a centralized database of instantiated virtualmachines, a virtual machine management system can efficiently andautomatically discover virtual machines by examining visible networkstorage units. If a virtual machine management system does not havevisibility into storage units of a network storage system or has limitedvisibility and access, then network storage units may be made visible bymodifying the network storage mapping and masking configuration. Forexample, a partition table on all visible network storage units may beexamined. A unique partition type, or other marker as discussedpreviously, may be used to facilitate automatic detection of thesenetwork storage units allocated for virtual machines. Within the contextof arrays, existing array-based masking and mapping primitives can beused to control access to virtual machines. Additionally, lockingcapability may be included within a portion (e.g., partition) of anetwork storage unit to allow multiple virtualization systems tocooperate when accessing a single VM.

FIG. 14 depicts a flowchart of an embodiment of a method for automaticdiscovery of virtual machines. At block 1401, attached network storageunits are detected. At block 1403, the detected units are scanned forvirtual machine markings and a list of the detected units with virtualmachine markings is generated. At block 1405, it is determined whetherthe list is empty. If the list is empty, then control flows to block1415. If the list is not empty, then control flows to block 1407.

At block 1407, one of the virtual machine marked units is selected fromthe list. At block 1409, virtual machine data is loaded from theselected network storage unit. At block 1411, the loaded data isexamined to identify any virtual secondary disk(s) and theircorresponding network storage unit(s). Any identified network storageunits are associated with the selected unit, and removed from the list.Of course, embodiments may mark network storage units that encodevirtual secondary disks or other non-state data differently. Hence,detect and scan operations, such as those depicted in blocks 1401 and1403, will yield a list of base network storage units. At block 1413,snapshot data and corresponding network storage units are identified.Any identified corresponding network storage units are associated withthe selected unit and removed from the list. At block 1414, anindication of the selected unit and associated units is encoded. Controlflows from block 1414 back to block 1405. If there are no remainingunselected network storage units in the list, then control flows toblock 1415. At block 1415, the encoding of discovered virtual machinesis indicated (e.g., presented via a user interface, stored in a file,etc.).

Moving a Virtual Machine

Instead of streaming pages of memory across an IP network, networkstorage system facilities can be leveraged to implement local move andremote move of a virtual machine. Moving a virtual machine locallytransitions virtual machine computations to a different virtualizationsystem, while maintaining data for the virtual machine in the samenetwork storage unit. Moving a virtual machine remotely transitionsvirtual machine computations to a different virtualization system andrelocates virtual machine data to a different network storage unit.

FIG. 15 depicts a flowchart of an embodiment of a method for performinga move of a virtual machine. At block 1501, the network storage unitsassociated with the virtual machine to be moved are determined. At block1503, candidate virtualization systems are identified. A set of storagearrays that encode the determined network storage units (e.g., LUNs) isdetermined, along with their target identifications. Virtualizationsystems that have visibility of the determined array and target IDs aredeemed suitable for hosting the virtual machine. At block 1505, one ofthe candidates is selected as a destination virtualization system. Atblock 1507, the determined network storage units are mapped to thedestination virtualization system. At block 1511, the virtual machine ismoved from the source virtualization system to the destinationvirtualization system. At block 1513, the network storage units areunmapped from the source virtualization system.

FIG. 16 depicts an embodiment of a local move command operation for avirtual machine. A virtual machine manager (e.g., on a virtualizationsystem, on a virtual machine management server, etc.) issues a movecommand to a virtualization layer of a source virtualization system. Themove command is also issued to a virtualization layer of a destinationvirtualization system. Responsive to receiving the command, thedestination virtualization system virtualization layer begins monitoringa network storage unit that encodes data of the virtual machine to bemoved. In addition to, or instead of, monitoring, the destinationvirtualization system may wait to receive a notification. The movecommand causes the virtualization layer of the source virtualizationsystem to begin paging out state data to the network storage unit. Thiscan be done in an incremental fashion. For example, dirty pages may betracked and re-synchronized iteratively. The source virtualizationsystem also indicates if a page includes new data in the network storageunit. Instead of, or in addition to, writing an indication into thenetwork storage unit, the source may inform the destination directly,(e.g., over an IP network). If the virtualization layer of thedestination virtualization system detects the new data indication, thenit requests the one or more new pages. Requested pages are then loadedinto the destination virtualization system by the virtualization layer.These operations repeat until a given limit is achieved. The limit maybe percentage of data paged out, time limit, user input, etc. Once thelimit is achieved, the virtualization layer of the source virtualizationsystem suspends the virtual machine. After suspending the virtualmachine, the source virtualization system indicates in the networkstorage unit that page out is complete. Upon detecting indication ofcompletion, the virtualization layer of the destination virtualizationsystem resumes the virtual machine in accordance with data loaded fromthe network storage unit.

As previously stated, the movement of a virtual machine may be across alocal-area network or a wide-area network. For network storage systemsthat support wide area replication (e.g., a SAN that supports wide-arrayreplication), the supported facility can be employed to implementmovement of a virtual machine across a wide-area network.

FIG. 17 depicts an embodiment of a remote move command operation for avirtual machine. A virtual machine manager issues a move command to asource virtual machine virtualization layer. The move command causes thevirtualization layer at the source virtualization system to trigger areplica of the data at a source network storage unit. The networkstorage system(s) for both the source and destination network storageunits perform a replication operation and copy all data from the sourcenetwork storage unit to the destination network storage unit. Thevirtualization layer at the source virtualization system then begins topage out state data to the source network storage unit. Upon achievingan update limit, the virtualization layer at the source virtualizationsystem triggers a replica update. The network storage system updates thedata in the destination network storage unit with new data from thesource network storage unit. The paging out of state data andreplication updates repeats until a limit for the move is achieved. Uponachieving the move limit, the virtualization layer at the sourcevirtualization system triggers a final replica update. After the finalreplica update, the virtualization layer at the source virtualizationsystem notifies a virtualization layer at a destination virtual machinehost. In response to the notification, the virtualization layer at thedestination virtualization system requests the data in the destinationnetwork storage unit for the virtual machine. Once the data has beenloaded into the destination virtual machine host, the virtualizationlayer at the destination virtualization system resumes the virtualmachine based on the loaded data. The virtual machine on the destinationvirtualization system may pre-warm its memory cache by reading part ofits cache while the data was being paged out from the sourcevirtualization system and prior to achieving the move limit.

Continuous data protection support may also be achieved by running themove command operations 24×7 without the final suspend/resume. Periodiccheck points may be implemented to ensure consistency of the memoryimage. The periodic check points may occur coincident with the replicaupdates. At any point in time, the virtual machine may be resumed at thedestination virtualization system based on the last coherent replica atthe destination network storage unit. A customer may be presented withtunable parameters to control how frequently these check-points areperformed, where the maximum setting requires all pages of memory to bewritten out constantly. The customer is then presented with a tradeoffof performance versus the time delay and potential for data loss as aresult.

Cloning

When a user wishes to create a clone of a virtual machine, a virtualmachine manager will trigger a snapshot as described above, and thenrequest the snapshots to be unlinked. With the capabilities of a networkstorage system, a virtual machine can be cloned expeditiously.

FIG. 18 depicts an embodiment of a clone operation for a virtualmachine. A virtual machine manager issues a clone command to avirtualization layer at a source virtualization system. The clonecommand causes the virtualization layer to trigger a replica of the dataat a base network storage unit. Data for the virtual machine beingcloned is copied from the base network storage unit to a clone networkstorage unit. The virtualization layer at the source virtualizationsystem then begins paging out state data to the base network storageunit. This repeats until a limit is achieved. As stated above, the limitmay be a percentage of data paged out, expiration of a time period, etc.Upon achieving the limit, an update replica is triggered. A replica ofupdates is made from the base network storage unit to the clone networkstorage unit. The virtualization layer of the source virtualizationsystem then notifies the virtual machine manager that page out andreplication is complete. Responsive to the notification, the virtualmachine manager causes identifying information for the virtual machineclone to be written into the clone network storage unit. The data storedin the clone network storage unit is updated with the ID of the clonenetwork storage unit, as well as unique identification information forthe clone virtual machine. For example, the update information includesBIOS UUID, MAC address, etc. The virtual machine manager maps the clonenetwork storage unit to the clone virtualization system. The virtualmachine manager then causes the clone virtualization system to activatethe clone virtual machine. The activation causes a virtualization layerat the clone virtualization system to request data for the clone virtualmachine from the clone network storage unit. The clone virtual machinethen begins operation based on the data loaded from the clone networkstorage unit.

Although the embodiment depicted in FIG. 18 illustrates paging out ofstate data, a clone command may replicate disk data as well. In oneembodiment, the clone command forces the source virtual machine to bestopped or powered off, and then copies the disk data of the virtualmachine. In another embodiment, the clone command causes the virtualmachine to be temporarily disabled (e.g., triggers a quiesce operation).A quiesce operation may be employed to preserve consistency in the filesystem of the operating system guest of the disabled virtual machine.Moreover, these methods for effectuating a clone command may also beemployed for effectuating a snapshot command.

Migrate

In addition to providing facilities for implementing current virtualmachine management commands, implementation of virtual machines withnetwork storage introduces additional management commands, such asmigrate. In general, it may be necessary, or desirable, to move data(e.g., a virtual disk) of a virtual machine to a different storage poolusing a migration facility.

FIG. 19 depicts a flowchart of an embodiment of a method for migratingvirtual machine data. At block 1901, a virtual machine and a destinationstorage pool are selected. At block 1905, corresponding network storageunits for the selected virtual machine are determined. At block 1907,configuration settings of the underlying storage system for the currentstorage pool of the selected virtual machine are determined. At block1909, it is determined if the configuration settings can be applied tothe underlying storage system of the selected destination storage pool.At block 1911, a different destination storage pool is elected if it isdetermined that the configuration settings cannot be applied to theunderlying storage system of the currently selected destination storagepool. Control flows from block 1911 back to block 1909. Otherwise, ifthe configuration settings can be applied, then the appropriate numberof network storage units are selected from the destination storage poolat block 1913. If network storage units have not been created in thedestination storage pool, then at least the proper number of networkstorage units are allocated from the destination storage pool to satisfymigration of the data for the selected virtual machine. At block 1914,I/O is routed to a new base network storage unit of the selected storageunits in the destination storage pool. Pending I/O requests are flushedout. At block 1915, the network storage units for the virtual machineare replicated to the network storage units of the destination storagepool. At block 1917, information in the new base network storage unitfor the virtual machine is updated to indicate the new correspondingnetwork storage units in the destination storage pool. In addition,information in the virtualization layer for the selected virtual machineis updated to reference the network storage units in the destinationstorage pool. The old network storage units may now be dereferenced anddeleted, returned to their storage pool, reassigned, etc.

The described embodiments may be provided as a computer program product,or software, that may include a machine-readable medium having storedthereon instructions, which may be used to program a computer system (orother electronic devices) to perform a process according to embodimentsof the invention, whether presently described or not, since everyconceivable variation is not enumerated herein. A machine readablemedium includes any mechanism for storing or transmitting information ina form (e.g., software, processing application) readable by a machine(e.g., a computer). The machine-readable medium may include, but is notlimited to, magnetic storage medium (e.g., floppy diskette); opticalstorage medium (e.g., CD-ROM); magneto-optical storage medium; read onlymemory (ROM); random access memory (RAM); erasable programmable memory(e.g., EPROM and EEPROM); flash memory; or other types of mediumsuitable for storing electronic instructions. In addition, embodimentsmay be embodied in an electrical, optical, acoustical or other form ofpropagated signal (e.g., carrier waves, infrared signals, digitalsignals, etc.), or wireline, wireless, or other communications medium.

Other Embodiments

While the invention(s) is (are) described with reference to variousimplementations and exploitations, it will be understood that theseembodiments are illustrative and that the scope of the invention(s) isnot limited to them. In addition, while our description ofvirtualization techniques has generally assumed that the virtualmachines present interfaces consistent with a hardware system, personsof ordinary skill in the art will recognize that the techniquesdescribed may be used in conjunction with virtualizations that do notcorrespond directly to any particular hardware system. Virtualizationsystems in accordance with the present invention, implemented as hostedembodiments, non-hosted embodiments or as embodiments that tend to blurdistinctions between the two, are all envisioned. Furthermore, variousoperations may be wholly or partially implemented in hardware. Forexample, a hardware implementation may employ a look-up table formodification of storage access requests to secure non-disk data.

Many variations, modifications, additions, and improvements arepossible, regardless the degree of virtualization. For example, whileparticular example operations were depicted for illustrative purposes,various techniques for exposing a network storage system and variousoperations for performing moves, migrations, clones, etc. of virtualmachines will also be appreciated by persons of ordinary skill in theart. Furthermore, while techniques and mechanisms have been describedusing particular network configurations, hardware architectures, memoryorganizations and particular operating system constructs (typicallyIA-32 based architectures/systems and Windows operations systems) as adescriptive framework, persons of ordinary skill in the art willrecognize other implementations can be envisioned for use in systemsthat support other processor instruction set architectures, othernetwork or memory configurations and/or other operating systemconstructs.

Plural instances may be provided for components, operations orstructures described herein as a single instance. Finally, boundariesbetween various components, operations and data stores are somewhatarbitrary, and particular operations are illustrated in the context ofspecific illustrative configurations. Other allocations of functionalityare envisioned and may fall within the scope of the invention(s). Ingeneral, structures and functionality presented as separate componentsin the exemplary configurations may be implemented as a combinedstructure or component. Similarly, structures and functionalitypresented as a single component may be implemented as separatecomponents. These and other variations, modifications, additions, andimprovements may fall within the scope of the invention(s).

What is claimed is:
 1. A computing system comprising: a first virtualmachine configured to execute on a first host; and a storage systemaccessible by the first host, the storage system including a pluralityof physical storage devices that are organized into a storage pool,which is a layer of abstraction for managing the physical storagedevices, wherein logical units of storage for storing virtual disks of aplurality of virtual machines including the first virtual machine,including a first virtual disk for the first virtual machine, areallocated from the storage pool, wherein, responsive to a first diskaccess request from the first virtual machine, which includes a locationwithin the first virtual disk to be accessed, at least one processor ofthe first host is configured to: generate a second disk access requestbased on the location within the first virtual disk to be accessed, thesecond disk access request including a location to be accessed withinone of the logical units of storage in which the first virtual disk isstored, determine whether or not access to the location to be accessedwithin said one of the logical units is permitted; and upon determiningthat the access to the location to be accessed within said one of thelogical units is permitted, transmit the second disk access request tosaid one of the logical units, and forward a response to the second diskaccess request from said one of the logical units to the first virtualmachine as a response to the first disk access request.
 2. The computingsystem of claim 1, wherein: upon determining that the access to thelocation to be accessed within said one of the logical units is notpermitted, the at least one processor of the first host is configured tonot transmit the second disk access request to said one of the logicalunits, and forward a notification that the first disk access request hasbeen denied as a response to the first disk access request.
 3. Thecomputing system of claim 2, wherein, responsive to the first diskaccess request from the first virtual machine, the at least oneprocessor of the first host is configured to determine that the accessto the location to be accessed within said one of the logical units isnot permitted when the location to be accessed within said one of thelogical units includes virtual hardware configuration data indicating aconfiguration of the first virtual machine.
 4. The computing system ofclaim 3, wherein the virtual hardware configuration data indicates anamount of virtual RAM in the first virtual machine, and a size of thefirst virtual disk.
 5. The computing system of claim 1, wherein each ofthe first and second disk access requests complies with an InternetSmall Computer System Interface (iSCSI) protocol.
 6. The computingsystem of claim 1, wherein said one of the logical units includes statedata for the first virtual machine and non-state data for the firstvirtual machine.
 7. The computing system of claim 1, wherein said one ofthe logical units includes only one of state data for the first virtualmachine or non-state data for the first virtual machine.
 8. A computersystem comprising: a host configured to execute a first virtual machine;a storage system accessible by the host, the storage system including aplurality of physical storage devices that are organized into a storagepool, which is a layer of abstraction for managing the physical storagedevices, wherein logical units of storage for storing virtual disks of aplurality of virtual machines including the first virtual machine,including a first virtual disk of the first virtual machine, areallocated from the storage pool; means for handling a first disk accessrequest from the first virtual machine, which includes a location withinthe first virtual disk to be accessed, said means for handling beingconfigured to: generate a second disk access request based on thelocation within the first virtual disk to be accessed, the second diskaccess request including a location to be accessed within one of thelogical units of storage in which the first virtual disk is stored,determine whether or not access to the location to be accessed withinsaid one of the logical units is permitted; and upon determining thatthe access to the location to be accessed within said one of the logicalunits is permitted, transmit the second disk access request to said oneof the logical units, and forward a response to the second disk accessrequest from said one of the logical units to the first virtual machineas a response to the first disk access request.
 9. The computer systemof claim 8, wherein the means for handling is further configured to:upon determining that the access to the location to be accessed withinsaid one of the logical units is not permitted, not transmit the seconddisk access request to said one of the logical units, and forward anotification that the first disk access request has been denied as aresponse to the first disk access request.
 10. The computer system ofclaim 9, wherein the location to be accessed within said one of thelogical units includes virtual hardware configuration data indicating aconfiguration of the first virtual machine.
 11. The computer system ofclaim 10, wherein the virtual hardware configuration data indicates anamount of virtual RAM in the first virtual machine, and a size of thefirst virtual disk.
 12. The computer system of claim 8, wherein each ofthe first and second disk access requests complies with an InternetSmall Computer System Interface (iSCSI) protocol.
 13. The computersystem of claim 8, wherein said one of the logical units includes statedata for the first virtual machine and non-state data for the firstvirtual machine.
 14. The computer system of claim 8, wherein said one ofthe logical units includes only one of state data for the first virtualmachine or non-state data for the first virtual machine.
 15. Anon-transitory computer readable medium comprising instructionsexecutable in a host in which a first virtual machines is configured torun, the host configured to access a storage system which includes aplurality of physical storage devices that are organized into a storagepool, which is a layer of abstraction for managing the physical storagedevices, wherein logical units of storage for storing virtual disks of aplurality of virtual machines including the first virtual machine,including a first virtual disk of the first virtual machine, areallocated from the storage pool, and wherein the instructions whenexecuted in the host cause the host to carry out a method of handling afirst disk access request from the first virtual machine, which includesa location within the first virtual disk to be accessed, said methodcomprising: generating a second disk access request based on locationwithin the first virtual disk to be accessed, the second disk accessrequest including a location to be accessed within one of the logicalunits of storage in which the first virtual disk is stored, determiningwhether or not access to the location to be accessed within said one ofthe logical units is permitted; and upon determining that the access tothe location to be accessed within said one of the logical units ispermitted, transmitting the second disk access request to said one ofthe logical units, and forwarding a response to the second disk accessrequest from said one of the logical units to the first virtual machineas a response to the first disk access request.
 16. The non-transitorycomputer readable medium of claim 15, wherein the method furthercomprises: upon determining that the access to the location to beaccessed within said one of the logical units is not permitted, nottransmitting the second disk access request to said one of the logicalunits, and forwarding a notification that the first disk access requesthas been denied as a response to the first disk access request.
 17. Thenon-transitory computer readable medium of claim 16, wherein thelocation to be accessed within said one of the logical units includesvirtual hardware configuration data indicating a configuration of thefirst virtual machine.
 18. The non-transitory computer readable mediumof claim 17, wherein the virtual hardware configuration data indicatesan amount of virtual RAM in the first virtual machine, and a size of thefirst virtual disk.
 19. The non-transitory computer readable medium ofclaim 15, wherein said one of the logical units includes state data forthe first virtual machine and non-state data for the first virtualmachine.
 20. The non-transitory computer readable medium of claim 15,wherein said one of the logical units includes only one of state datafor the first virtual machine or non-state data for the first virtualmachine.